1. Technical Field
The invention relates to vibration damping devices and systems which develop a controllable, user-adjustable damping-force when applied between two moving members, for applications such as automobile suspensions, industrial machinery, or other equipment. More particularly, the invention relates to a hydraulic damping system which uses a field responsive fluid such as an electrorheological (ER) fluid as the medium for controlling the damping performance of the device.
2. Background Information
In automotive vehicles and in other types of equipment which are subjected to vibration and shocks, various devices and systems are used to dampen, or lessen, the effect of the vibration. In automotive vehicles, vibrations are caused by traveling over road protrusions or depressions and are transmitted from the road surface, through the suspension, to the vehicle body. Vibration damping devices placed between the vehicle suspension and body are commonly used to damp these vibrations to maintain control of the vehicle and provide a smoother ride for occupants of the vehicle.
Typical automobile dampers are axially-sliding, oil-filled, hydraulic devices that produce a velocity dependant resistive, or damping force as they are compressed or extended. The damping force is generated via viscous/turbulent dissipation mechanisms associated with the flow of the hydraulic fluid through valves and passageways inside the damper.
Although such conventional devices have proven satisfactory for most applications, attempts to further refine ride-quality, while maintaining vehicle control, have identified a need for a damper with adjustable damping performance. In conventional hydraulic dampers, this tuneability is achieved by modifying the geometry of the flow-path. For example, an external motor may be connected to mechanisms within the damper such that motion of the motor alters the size of a metering orifice and/or the preload on a valve. In typical applications, an on-board computer monitors body and suspension motions to calculate an optimum damping performance and issues a control signal so that the damper is adjusted to the desired state.
A more recent development has evolved in which an electrorheological (ER), or field-responsive fluid is used within the chamber of the damper. One or more electrodes are provided within the device such that an applied voltage effects an increase in the ER fluid""s viscosity. Since the fluid""s viscosity varies in proportion with the intensity of the applied voltage, adjustability of damping performance is achieved by altering the physical properties of the fluid in the damper rather than the geometry of the flow path. In practice, this allows for a damper which can respond to a control signal more quickly than a conventional adjustable damper. U.S. Pat. Nos. 5,180,145; 5,316,112 and 5,366,048 are examples of such devices.
For certain applications, it has been found desirable to combine the known, durable construction of a conventional hydraulic damper with the adjustability and fast response of an ER damper. In such hybrid units, the damping energy is dissipated by viscous/turbulent dissipation mechanisms associated with the flow of the hydraulic fluid inside the damper. ER fluid is used in a separate control element to alter the characteristics of the flow path through which the hydraulic oil circulates. With proper design and placement of the control element, many of the ER damper""s desirable properties can be maintained. Some examples of controllable hybrid dampers using an ER control fluid are shown in U.S. Pat. Nos. 5,161,653 and 5,752,891.
Although these prior art, hybrid dampers provide satisfactory solutions for certain applications, they possess several shortcomings. For example, U.S. Pat. No. 5,161,653, which is believed to be the closest prior art to that of the subject invention, discloses a hybrid ER/hydraulic fluid damper. However, the ER control element of this damper does not permit an increase in damping force during the course of a stroke beyond that which is achieved at time that the control element is energized. This means that in order to effect a maximum force response, the control element must be energized precisely at the end of a stroke when there is no flow. Consequently, if the system is not fast enough to react to an event, damping performance is compromised until the direction of the stroke is reversed. Therefore, it is desirable to provide a hybrid ER/hydraulic fluid damper in which the damping force can be controlled independently of other operating parameters such as stoke direction, velocity, frequency, or amplitude.
Objectives of the invention include providing an improved damping device and system using a field responsive fluid, such as an electrorheological and/or magnetorheological fluid, preferably of the type suitable for a vehicle suspension system, which solves the aforementioned problems of prior art hybrid ER/hydraulic dampers by providing a system that is fast enough to react to various forces exerted on the vehicle or equipment and which requires a relatively small amount of ER fluid and which does not subject such fluid to a harsh environment as in those dampers wherein the ER fluid is the main fluid contained within the piston chamber.
A further objective of the invention is to provide such a damping system which is able to independently change the magnitude of the damping force during the course of the stroke and in which the response time is in the millisecond time-frame, thereby enabling control of individual wheel motions in an automobile or similar vehicle.
A still further objective of the invention is to provide such a damping system which is significantly less costly than an electromechanical valve system that can respond in a similar time period, and in which a field responsive fluid cell containing the ER fluid is placed outside of the path of the main hydraulic fluid and can be serviced and/or replaced easily without affecting the integrity of the main body of the hydraulic damper.
A further objective of the invention is to provide such a damping system which has relatively few moving parts which are exposed to the ER fluid, and which requires a minimum amount of field responsive fluid and is therefore less expensive to construct and maintain.
Another objective of the invention is to provide such a damping system which is similar in many respects to conventional hydraulic dampers as to size and means of attachment to the vehicle thereby enabling the damping system to be utilized in existing spaces intended for conventional type hydraulic dampers yet is able to provide the desired versatilities of dampers required to contain the ER fluid as the replacement for the heretofore hydraulic fluid.
A further objective of the invention is to provide such a damping system which is of a rugged, compact, relatively lightweight simple design and which achieves the stated objectives in a simple and efficient manner.
These objectives and advantages are obtained by the improved vibration damping system of the present invention, the general nature of which may be stated as including a hydraulic damper including a housing forming an internal hydraulic fluid chamber and a damping member slidably reciprocating within said chamber and dividing said chamber into a pair of subchambers, said damping member being adapted to be connected to a first support structure; connection means on the housing for connecting said housing to a second support structure spaced from said first support structure; a hydraulic motor in fluid communication with the hydraulic damper for controlling the movement of hydraulic fluid between the subchambers upon movement of the damping member within the fluid chamber; a fluid line providing the fluid communication between the hydraulic motor and the fluid subchambers, said motor being mounted in said fluid line which said hydraulic fluid flows through said motor; and a flow cell adapted to contain a field responsive fluid operatively connected to the hydraulic motor for controlling the amount of damping of the vibration damper by controlling the hydraulic motor by regulating the amount of pressure required to pass a fixed amount of hydraulic oil through said hydraulic motor.